package com.work.demo.controller;

import lombok.extern.slf4j.Slf4j;

/**
 * @Description 唯一Id生成器基于雪花算法
 * @Author jie.zhao
 * @Date 2019/8/15 11:58
 */
@Slf4j
public class SnowFlakeUtil {

	private static SnowFlakeUtil flowIdWorker = new SnowFlakeUtil(1);
	private final long id;
	/**
	 * 时间起始标记点，作为基准，一般取系统的最近时间
	 */
	private final long epoch = 1524291141010L;
	/**
	 * 机器标识位数
	 */
	private final long workerIdBits = 10L;
	/**
	 * 机器ID最大值: 1023
	 */
	private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;
	/**
	 * 毫秒内自增位
	 */
	private final long sequenceBits = 12L;

	/**
	 * 12
	 */
	private final long workerIdShift = this.sequenceBits;
	/**
	 * 22
	 */
	private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;
	/**
	 * 4095,111111111111,12位
	 */
	private final long sequenceMask = -1L ^ -1L << this.sequenceBits;
	/**
	 * 0，并发控制
	 */
	private long sequence = 0L;
	private long lastTimestamp = -1L;

	private SnowFlakeUtil(long id) {
		if (id > this.maxWorkerId || id < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
		}
		this.id = id;
	}

	public static SnowFlakeUtil getFlowIdInstance() {
		return flowIdWorker;
	}

	/**
	 * 获得系统当前毫秒数
	 */
	private static long timeGen() {
		return System.currentTimeMillis();
	}

	public static void main(String[] args) {
		for (int i = 0; i < 100; i++) {
			SnowFlakeUtil snowFlakeUtil = SnowFlakeUtil.getFlowIdInstance();
			System.out.println(snowFlakeUtil.nextId());
		}
	}

	public synchronized long nextId() {
		long timestamp = timeGen();
		if (this.lastTimestamp == timestamp) {
			//如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环); 对新的timestamp，sequence从0开始
			this.sequence = this.sequence + 1 & this.sequenceMask;
			if (this.sequence == 0) {
				// 重新生成timestamp
				timestamp = this.tilNextMillis(this.lastTimestamp);
			}
		} else {
			this.sequence = 0;
		}

		if (timestamp < this.lastTimestamp) {
			log.error(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
			return -1;
		}

		this.lastTimestamp = timestamp;
		return timestamp - this.epoch << this.timestampLeftShift | this.id << this.workerIdShift | this.sequence;
	}

	/**
	 * 等待下一个毫秒的到来, 保证返回的毫秒数在参数lastTimestamp之后
	 */
	private long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}
}
